Self-priming siphon drain



1962 J. N. PIROK ETAL 3,019,806

SELF-PRIMING SIPHON DRAIN Filed Feb. 1'7, 1960 Zvvzwroms JOHN A! P/Ro/r Jon /7. 7/:"AMMELL BY 4 fla w'ye ti -"I United States Patent Ofifice 3,019,806 SELEPRIMING SHE-EON DRAIN John N. Pirok, Evergreen Park, and Joel H. Trammeii,

Chicago, 111., assignors to (Ihicago Bridge 8: iron Company, tlhicago, 111., a corporatian of lliinois Filed Feb. 17, 1961), Ser. No. ,235 14 Ciaim's. (El. 137-142) This invention relates to anapparatus for removing the liquid contents of an elevated storage tank which are trapped in portions of the tank below the outlet means from the tank. It is more particularly concerned with a self-priming siphon for a storage tank having areas of so-called' dead storage.

One of the most important factors in the design of large elevated storage tanks is the requirement that the metal tank bottom and side Walls be worked to the highest stresses compatible withconservative standards of safety. This object can best be achieved by selecting a tank design which permits the tank bottom and side walls to work exclusively in tension and not at all in bending. In tank designs of this nature a system of membrane stresses is produced. In order to produce menu brane stresses rather than bending stresses in metal con-- tainers for liquids, however, it is necessary either that the metal be continuously supported on the surface opposite the surface containing the stored liquid or else that the conformation of the metal between supports be curved or dished.

It is uneconomical to provide an elevated support structure for a liquid storage tank which provides continuous support for the metal of the tank proper, and for that reason designs are selected which provide intermittent supports of various types. One of the most economical designs for providing intermittent support is the so-called toroidal bottom design. Primary drainage of the tank is effected generally by employing a so-calied wet. riser pipe which serves as the liquid conduit for filling and draining the tank for separate piping arrangements for this purpose contained within a dry riser which. serves as a casing. for the piping. Storage tanks employing a toroidal bottom design are described and claimed. in copending United States application Serial No. 764,861, filed October 2, 1958 of Clarence D. Miller and John N. Pirok, entitled Elevated Storage Tank, now Patent No. 2,961,118.

This design has a disadvantage, however, inthat it results in areas of dead storage below the tank outlet in the toroidal bottom in which liquid stored in the tank. ordinarily will remain under normal gravity drainage conditions. These areas of the toroidal bottom therefore cannot be utilized as effective storage capacity. Moreover, if liquid in this dead storage area is not withdrawn, a difficult tank cleaning and maintenance problem results because of the inability to.obtain a dry tank bottom without resorting to cumbersome or expensive expedients'. It is not usually feasible to provide a simple drain from the lower-most portion of theta'nk bottom either to the ground or to the tank riser pipe, primarily because of the possibility of freezing in most locations within the temperateor colder zones.

According to this invention. there is provided a siphon age for withdrawing water stored in the lower-most portions of an elevated tank bottom. The siphon apparatus of this invention is provided witlr a self-priming feature so as to enable the siphon to operate automatically and thereby permit the use of the liquid so withdrawn by means of the siphon ,as effective usable liquid in the storage system. Other objects of the inventionwill' appear from the detailed dislosure which follows.

FIGURE 1 is a vertical cross-sectional view of anti lustrative elevated storage tank having a toroidal bottom in which the selfpriming siphon of this invention is used.

FIGURE 2 is avertical cross-sectional view of an elevatedstorage tank having a. toroidal bottom in which another embodiment of the novel self-priming siphon of this invention. is.- employed.

FIGURE 3 is a sectional representation of an irregularly dimensioned embodiment of. the invention.

Referring. to FIGURE 1,- the storage tank 14? is elevated above the: groundv by means of columns 12 which, as shown, are located peipherally belowthe outermost circumference of the tank and connected thereto at the equator of the tank. The tank has spheroidal or toroidal side walls 13, a toroidal bottom 14 depending below the tank outlet located at. the upper terminal end of riser 15, and a roof 16 which may be a segment of a sphere or other suitable shape. Central wet riser pipe 16 extends from ground level to an intersection with the toroidal bottom for the purpose of providing inlet and outlet means for liquid to be stored in the tank. A siphon 17 having certain. specific dimensional relationships as described hereinv is mounted. on the interior of tank 10 by means of suitable brackets 18 fitted to the interior of bottom. 14 and riser 15. Siphon. 17 has an inlet leg 19 depending into the bottom 14, a horizontally disposed connector 20, and a priming leg 21. installed within the riser pipe 15.

In the embodiment shown in FIGURE 1, the inside diameters of all portions of the siphon are equal, such that the diameter of the priming leg 21, d equals the diameter of the connector 20, d Other siphon systems, however, can be used in accordance with this invention in which the diameter of the siphon components differ.

In its operation, the subject siphon can be described as working in three stages, as follows.

Stage 1.As liquid is introduced into the central riser pipe 15, it is pumped upwards and is confined to the riser pipe 15 and to the priming leg 21 of siphon 17 until the liquid reaches the riser outlet at the intersection of the riser 15 and the tank bottom 14, at which time the level of liquid in the riser pipe 15 is exactly equal to the level of liquid in the priming leg 21 because the air pressure on each liquid surface is the same.

Stage 2'.As liquid continues to be pumped through riser pipe 15 into tank 10, it flows over the intersection between the riser and the tank bottom, filling the dished area of the tank botom 14 depending below the outlet in riser pipe 15-, and also fi'ows into the inlet leg 19 of thesiphon. When the level of the liquid in the riser 15 and the tank bottom 14 reaches the level of the intersection of'the riser 15 and the bottom 14, there is liquid in. both the inlet leg 19 and the priming leg 21 of the siphon at a level substantially equal to (but theoretically somewhat lower than) the level of liquid surrounding those legs, but the portion of. the siphon forming the connector 2.0 in the shape of an inverted U above this level is filled with air which is now sealed against escape as the liquid level continues: to rise. As the filling of the tank continues, the liquid level in both the inlet leg 19 and the priming leg 21 of the siphon continues to try to rise but the pressure of the air in the connector portion 20 of the siphon prevents any significant further rise from taking place. as generally indicated in FIGURE 1, this condition of compressed air in the connector portion 20 of the siphon is at its maximum pressure.

As liquid is withdrawn from the tank, there is no further effect upon the liquid or the air in the siphon except that. the pressure of air above the inlet and priming legs 19 and 2 1. is reduced commensurately with the reduction of height of liquid in the tank. This condition continues Patented" Feb. 6, 19b2- When the tank 10 is filled to its capacity,

until the level of the liquid reaches the level of the intersection between the riser and the tank bottom 14.

Stage 3.-Continued draw down of liquid in riser 15 lowers the liquid in the priming leg 21 commensurately, creating a partial vacuum in the air space in connector above the liquid and thereby drawing in liquid to the inlet leg 19 of the siphon from the dished portion of the bottom 14. When the level of liquid in the inlet leg 19 reaches the level of the connector 20, the siphon is primed. Thereafter, liquid flows across through connector 20' from the inlet leg 19 to the priming leg 21 and down into the riser. As the liquid level continues to be dropped, the increasing difference in elevation between the level of liquid in the dished portion of the bottom 14 and the riser 15 causes the rate of flow of liquid from the siphon to increase.

In FIGURE 1 certain symbols have been added to give essential dimensional relationships in establishing the design of a single diameter siphon, as follows:

A cross-sectional area of the pipe;

I is the height of the horizontal conector 20 above the level of the intersection of the riser 15 and the bottom 14;

K is the horizontal distance between the inlet leg 19 and the priming leg 21 of the siphon;

L is the minimum length of the priming leg 21 measured from its lower end to the level of the intersection between the riser pipe 15 and the bottom 14;

M is the length of the inlet leg 19 of the siphon measured from its lower end to the level of the intersection between the riser 15 and the bottom 14; V

N is the vertical distance from the outlet of inlet leg 19 to the inlet of horizontal connector;

d is the inside diameter of the priming leg 21 of the siphon;

d is the inside diameter of the other portions of the siphon, including connector 20 and inlet leg 19; and

R is the height of a rise along connector 20 from inlet 19 to priming leg 21.

All length dimensions of the siphon except L are determined by the physical characteristics of the tank and the layout of the siphon therein. The minimum length of the priming leg L, however, is determined in the following manner.

According to Boyles law, P V =P V In stage 2, as described above, the volume of air within the siphon above the level of the intersection of the riser 15 and the bottom 14 is V Therefore, V =A(M+S) where A is the area of the pipe and S=K+N+J. The pressure of the air in the pipe is P In stage 3, as described above, the volume of air in the siphon above the water surface is V which equals A(L-Ml).

More specifically, when siphoning begins, the height of the water column in the priming leg 21 extends above the level of water in riser 15 by a distance equal to the height which water in the tank bottom 14 must be raised before siphoning can begin. This latter height is M+J. The numeral 1 represents an additional one foot of length added to leg 21 to assure a head of water in leg 21 when the water level in riser 15 drops below the level at which siphoning just starts. When siphoning is read to start, leg 19 and connector 20 are filled with water; and leg 21 contains water in its lower portion for a height equal to the one foot thereof below the water level in riser 15 plus the height which the water from the bottom of tank 14 was raised, i.e., 1+M+]. Accordingly;

pheric pressure at the level of the tank installation. The difference in pressure between P and P must besuch Accordingly V V 0.434(J+M) Substituting the values for V and V above:

where L, S, M and I are in feet. In practice, the actual length of the priming leg 21 is made several feet longer than L in order to assure a full priming of the siphon. For example in atypical installation employed in a 1,500,000 gallon tank the single diameter priming leg of a siphon constructed from 2"-4 pipe, as calculated, would be 33' long. In order, however, to compensate for atmospheric pressure changes and pipe friction losses 8 is added to the length of the priming leg to provide an overall length of 41'.

In some installations, depending upon the diameter of the priming leg, a throttling means or restrictor 25 shown in FIGURE 1 is mounted on the free end of the priming leg in order to insure against breaking the siphon under free fall conditions. This can be provided by affixing a conventional pipe reducer or other suitable fiow control means to the priming leg. Generally no restriction is required if 2" pipe is employed for the priming leg of a single diameter siphon. If 3" or 4" pipe is used a 2 /2. restrictor will function effectively to reduce the outflow of the priming leg.

In the event that the tank design requires the use of long horizontal runs of pipe to connect the inlet leg 19 and the priming leg 21, horizontal connector 20 should slope upwardly toward the priming leg. A rise R of about two pipe diameters will generally provide sufiicient slope to the horizontal connector.

This rise assures a closed channel type of flow when the siphoning is initiated, which, in turn, prevents a break in the flow of water through the siphon.

Without this rise, there would be a gap between the top of the liquid flowing out through connector 20 and the top of the connector inner surface. The air in the space created by this gap could cause a disruption in the flow of liquid through the siphon when the liquid level in riser 15 drops below the lower end of leg 21.

To illustrate the instant invention a single diameter self-priming siphon drain of this invention was installed in a 1,500,000 gallon elevated water storage tank of the type shown in FIGURE 1. The toroidal bottom contained 42,000 gallons of dead storage. To empty the dead storage two single diameter 'siphonsconstructed from conventional 3" steel pipe were diametrically mounted in the interior of the tank. The horizontal connector was installed 1 above the cusp formed by the intersection of the toroidal bottom and the flared transition section of the riser. The connector which was 25.5 long sloped upward 6 toward the priming leg. An inlet leg 2.17 long was connected to the connector leg by a conventional elbow fitting and depended downwardly to within 2" of the tank bottom. A 41' priming leg was similarly connected to the other end of the connector leg. A 2 /z"x3" pipe reducer was connected to the free end of the priming leg to function as a restrictor. In use these siphons functioned satisfactorily in emptying the dead, storage portion of the tank.

An alternative design for an elevated water storage tank is shown in FIGURE 2 wherein an'inwardly sloping inlet leg 26 is used. In this ar-Ifingement O is the length of inlet leg 26 and the other dimensions are as hereinbefore noted;

From the foregoing analysis it can be seen that the dimensions of the siphon depend, among other things, upon the density of the liquid being storedand the diameters of the tubes employed in fabricating the inlet leg and connector and thepriming leg. While the foregoing equation is a solution for the dimensions where water is the liquid being stored, and where "the pipes have circular cross-sections, similar equations can be developed for other liquids and cross-sectional shapes.

FIGURE 3 shows sectionally an irregularly sioned siphon, to illustrate another embodiment in which the internal sectional dimensions of the priming leg L vary. For such a general case it becomes impossible to adhere to all the symbols used hereinabove. The printing leg L with a diameter, d has a-complementary portion 27 with a smaller diameter, ti I, K, M and N are, respectively, the dimensions hereinbefore defined.

To determine the required length of priming leg '21 for use in an elevated water storage tank service dimen- 6 up .of more than one toroidal section thereby providing two or more areas to be drained; where in a tank installation a dry riser is employed which does not terminate at the 'lowest level of the bottom, but terminates at the lowest level of a dished head which is suspended above the main part of the bottom, or combinations of one or more of the other examples.

The illustrative siphon arrangement, although shown in ,a wet riser construction, can be utilized in dry riser assemblies provided an outlet-inlet pipeof sufiicient diameter is employed. Also, one or more siphons spaced about the riser can be used to facilitate tank drainage. Other modifications can be also made without departing from the scope of this invention.

Accordingly, it is intended that the instant invention be limited in the manner set forth in the appended claims.

What is claimed is:

1. In --a tank for liquid storage having a riserpipe penetarting' the bottom of said tank, said riser pipe including means for introducing and removing water from said tank, :said bottom having an obstruction preventing a portion of the "bottom from being drained, a siphon for draining that bottom portion of the tank, said siphon 1. comprising an inlet leg' extending into said bottom portion, a connecting leg in communication with said inlet leg, and :a priming leg in communication with said connecting leg freely depending into said riser pipe, said siphon being :of such dimensions that the length of said priming leg is not less than:

othersterner:ar

Priming leg 21 has a smaller diameter tail pipe 28 to tain siphon conditions.

In the construction of siphons employed in this invention conventional materials of construction can be employed depending upon the characteristics of the liquid being stored. For conventional liquids cylindrical pipes having diameters within the range of 1 /2 to 8 inches for use in storage tanks having capacities up to about 1,000,000 gallons are generally used. Other diameters, however, can be used depending upon the design requirements.

It is obvious from the foregoing detailed description that variations may be made in some details of the invention without departing from its scope as defined in the appended claims. For example, cylindrical pipe is shown, but polygonal or other pipe may also be used; and an inverted V or an irregular shape may be used instead of the inverted U shown and described in the connector. For most practical purposes, at low altitudes, the value 14.7 may be assigned to P in the foregoing equations. Although this invention is specifically illustrated in its preferred application to toroid-al bottom tanks wherein the riser pipe terminates at the bottom portion, it is obvious that it can be employed in any tank installation wherein dead storage spaces within the tank are created by the riser pipe terminating within the interior of the tank above the intersection of the tank bottom and the wall of the riser pipe or bya part of the bottom forming an obstruction preventing a portion of the bottom from being drained. This latter situation occurs, for

example, when the larger spheroidal elevated tanks are supported on two rows of columns or on a fluted riser at the center; where in a large tank, the bottom is made connecting leg at the end adjacent said priming leg above the level of the riser opening plus the height (N) in feet {f at the other end of said leg adjacent the inlet leg above which the restnctor 29 is attached, I tl to l the level of the riser opening, P is the usual'atmospheric pressure at the level of saidtank in pounds .per square inch, and M is the distance in feet measured from the bottom opening of the inlet leg to the riser opening.

2. In an elevated tank in accordance with claim 1 in which said priming leg has sufficient additional length to compensate for atmospheric pressure changes and pipe friction losses.

3. In an elevated tank in accordance with claim 1 in which the end of the connecting leg adjacent said priming leg ishigher than the end thereof adjacent said inlet leg.

4. In an elevated tank in accordance with claim 1 in which the free end of said priming leg is provided with a throttling means constructed to maintain siphoning conditions within said priming leg during use.

5. In a tank for liquid storage having a riser pipe penetrating the bottom of said tank, said riser pipe including means for introducing and removing water from said tank, said bottom having an obstruction preventing a portion of the bottom from being drained, .a siphon for draining said bottom portion, said siphon comprising an inlet leg inwardly sloping into said bottom portion at an angle to the horizontal, a connecting leg in communication with said inlet leg, and a priming leg in communication with said connecting leg, depending freely into said riser said siphon being of such dimensions that the length of said priming leg is not less than:

Where the length of said priming leg is measured in feet from its bottom opening to the level of said intersection,

Q is the pressure in pounds per square inch of a one foot high column of stored. liquid, S is the length (K) in feet of said connecting leg, plus the height (I) in feet of said connecting leg at the end of the connecting leg adjacent the priming leg above the level of said intersection, plus the length in feet of said inlet leg measured from its bottom opening to-the connection with said connecting leg where:

+N sine M equals the vertical distance in feet between the bottom opening of said inlet leg and the riser opening, N equals the vertical distance in feet between the riser opening and the intersection level of the inlet leg, and P is the usual atmospheric pressure at the level of said tank in pounds per square inch.

6. In an elevated tank in accordance with claim 5 in which said priming leg has suficient additionallength to compensate for atmospheric pressure changes andpipe friction losses.

7. In an elevated tank in accordance with claim 5 in which the end of the connecting leg adjacent said priming leg is higher than the end thereof adjacent said inlet leg.

8. In an elevated tank in accordance with claim 5 in which the free end of said priming leg is provided with a throttling means constructed to maintain siphoning conditions within said priming leg during use.

' 9. The siphon of claim 1 adapted for use in an elevated water storage tank in which the value of Q is 0.434.

10. The siphon of claim 5 adapted for use in an elevat said siphon being of such dimensions that the length of said lower portion of said priming leg is not less than:

M+N sinB plus the vertical length (J) in feet of said priming leg measured from its intersection with the connecting leg to the riser opening, M being the vertical distance in feet betweenthe bottom opening of the inlet leg and the riser opening, N being the vertical distance in feet between the riser opening and the intersection level of the inlet leg and P is the usual atmospheric pressure at the level of leg angularly, depending into the said bottom portion at an angle 9 with the horizontal a connecting leg in communication with said inlet leg, and a priming leg having an upper portion with an inside diameter d in'communication with said connecting leg, and a lower'portion having an inside diameter d depending from said upper portion,

said tank inpounds per square inch.

12. In an elevated, tank in accordance with claim 11 in which said priming leg has sutficient additional length to compensate for atmospheric pressure changes and pipe friction losses.

13. In an elevated tank in accordance with claim 11 in which the end of the connecting leg adjacent said priming leg is higher than the end thereof adjacent said inlet leg.

14. In an elevated tank in accordance with claim 11 in which the free end of said priming leg is provided with a throttling means constructed to maintain siphoning conditions within said priming leg during use.

References Cited in the file of this patent UNITED STATES PATENTS 2,603,534 Miller July 15, 1952 2,884,942 Caldwell et al. May 5, 1959 FOREIGN PATENTS 328,429 Italy Aug. 8, 1935 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,01%806 February 6 1962 John N, Pirok et al.

It is hereb certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 2, line 11 q for "peipherally" read peripherally line 47 for "b'otom" read bottom column 3, line 62 for "read" read ready column 6 lines 18 and l9 for "penetarting" read penetrating line 66, for "angle to" read angle 6 to Signed and sealed this 12th day of June 1962.

(SEAL) Attest:

DAVID L. LADD ERNEST W. SWIDER Commissioner of Patents Attesting Officer 

